Controllable electron discharge tube having low tube losses



July- 3, 1951 w; G. BROWN 2,559,395

CONTROLLABLE ELECTRON DISCHARGE TUBE HAVING LOW TUBE LOSSES Filed July 15, 1948 2 Sheets-Sheet 1 FIG-.1. 516.2. f d

as as 5 w 54 s c- '11 /E E 14 .r A1 A! "MIk II VENTOR. 11/. /& 293mm July 3, 1951 w; G. BROWN 2,559,395

CONTROLLABLE ELECTRON DISCHARGE TUBE HAVING LOW TUBE LOSSES Filed July 15, 1948 2 Sheets-Sheet 2 1 .VV EN TOR.

4'9 4, MMM

WATToRNEY Patented July 3, 1E

CONTROLLABLE ELECTRON DISCHARGE TUBE HAVING LOW TUBE LOSSES Warren G. Brown, West Englewood, N. J., as-

signor to Electrons, Incorporated, Newark, N. L, a corporation of Delaware Application July 15, 1948, Serial No. 38,784

(i'Jl. 313-153) 15 Claims.

1 .his invention relates to electron discharge LuuBS of the high vacuum type, and more particularly to tubes of the triode type affording control of the anode current by a grid or equivalent need not necessarily have a high positive potential. The flow of current in the external output circuit of a tube is due to the fact that an electrode connected to such circuit is receiving eleccontrol element. 5 trons carrying electrical charges at a certain In various applications of grid control high rate, i. e., 628x electrons per second per vacuum tubes, and more particularly in the field ampere of current. Such rate of accumulation of power conversion devices, the losses in the of electrons corresponds with the product of the tube are an important factor affecting the rating concentration or volume density of the electrons and efiicient use of the tube. Considering a tube 10 and their velocity. A given current to an elecas a circuit element, the losses in the circuit due trode may be obtained from a high density of low to the tube are represented by the product of the velocity electrons just as well as from a low current being conducted and the anode to cathdensity of high velocity electrons, so that it is ode diflerence of potential or tube drop voltage not essential for this electrode to have a high during the conduction period; and it is evident 16 potential and impart high velocity to the electhat any reduction in the tube drop voltage for a trons it receives. If electrons are available in given conduction current means a decrease in sufficient density near the surface of an electrode, the losses through the tube and an increase in its this electrode may have a low potential and still eiiiciency as a circuit element. When a tube concollect electrons at the desired rate for output ducts current, the kinetic energy of the elec- '20 current from the tube.

trons arriving at the anode due to the velocity In the usual arrangement of tube elements for they acquire under the influence of the tube drop a controllable electron discharge tube, such as voltage is converted into heat when the electrons exemplified in the conventional triode, the space strike the anode; and the ability of an anode to current in the tube is established principally by dissipate such heat of electron impact or bomthe positive potential on the anode with respect bardment, together with the heat radiated to it to the cathode, since a positive potential on the from the hot cathode, is a significant factor afgrid causes electron current to the grid and obfecting the rating of the tube and it applicajectionable grid circuit losses, as well as diverttion or use. While tube losses and efficiency may ing from the anode a substantial part of the addibe of minor importance in many applications and tional space current obtained by making the grid uses of controllable electron discharge tubes. in positive. In other words, in the conventional comparison with other desirable operating chartriode one electrode acts to establish the space acteristics, such as linear response for the comcurrent as well as receive it, and the control elecmunication field, small tube losses and high plate trode 0r grid merely Serves o Control this Space efficiency become significant and important current. Under such conditions, the anode to where such tubes are used in power conversion cathode difference of potential or tube drop voltapparatus, such as power oscillators, inverters age is dictated by the e ect o potential and the like. quired to establish the desired space current. The operation of a controllable electron dis- The anflde t0 Cathode pac d ar y ne d d charge tube in its broader aspects involves two in a conventional triode to take care of the intersomewhat distinctive functions, first the creation e n r d and P ov de t pp p mechanof a controllable space current in the tube, and ical separation of the parts, calls for a relatively. second the accumulation or collection of elechigh ub p a e, a d hence c p dtrons from this space current by a suitable elecingly lar 0 88 in e ub 80, th a ode 111 trode to provide current in the external output a conventional triode receives electrons at high circuit of the tube. The electrode potential revelocity and low density. If the velocity of the quirements for these functions are different. electrons at the anode surface can be reduced The creation of space current in a tube inherwith a corresponding increase in density, the ently requires a high positive electrode potential same current may be conducted by the tube with with respect to the cathode to draw electrons less heating of the anode, since the kinetic enfrom the emissive surface of the cathode and ergy of the electrons to be absorbed by the anode accelerate them through a region of space charge increases with the square of their velocity, while to the appropriate velocity to form a space curfor a given current the electron density varies rent. An electrode to collect or accumulate elecdirectly with a change in velocity. trons from an existing space current, however,

In the conventional tube structure having these characteristics and limitations, the velocity and direction of movement of the electrons emitted from the cathode are determined primarily by the existing electrostatic field established by the electrode potentials. An electron in motion under the influence of an electrostatic field, however, may also have its direction of movement influenced by a magnetic field; and a magnetic field may be utilized in combination with an electrostatic field to direct or focus electrons along certain paths or trajectories without changing the kinetic energy or total velocity imparted to such electrons by the electrostatic field.

With these and other considerations in mind, it is proposed in accordance with this invention to combine a magnetic field with the electrostatic field of electrode potentials in a controllable electron discharge tube in such a way that the current conducted by the tube may be cut off and controlled in intensity by a control element in a manner comparable with the conventional triode, but also such that the tube will conduct this current in operation with a tube drop voltage and tube losses much lower than in the conventional triode.

Generally speaking, and without attempting to define the nature and scope of the invention, a suitable source of magneto-motive-force providing a magnetic field is utilized in a distinctive structural arrangement :or organization of a thermionic emissive cathode, control element and anode to provide a tube in which the potentials on the control element serve to establish as well as control the space current to be conducted by the tube, largely independently of the anode potential, and without material or objectionable electron current to such control element in spite of its positive potentials, and in which the space current under the control of said. control element may be received by the anode in the operation of the tube with a relatively low anode to cathode difi'erence of potential or tube drop voltage, and with low tube losses and electron bombardment of the anode.

Various other objects, attributes, characteristic features and advantages of the invention will be in part apparent, and in part pointed out as the structure and mode of operation of certain specific embodiments of the invention are hereinafter described.

Although the controllable electron discharge tubeof this invention may take a wide variety of structural forms, it is convenient in discussing the principles and mode of operation characterizing the invention to refer to some specific tube structure; and for this purpose there is illustrated schematically in the accompanying drawings on'e specific organization and arrangement of parts as a typical embodiment of the invention.

In these drawings, Fig. 1 is a longitudinal section through the tube and associated magnetizing coil in one plane; Fig. 2 is a longitudinal section in another plane along the line 2-'2 of Fig. 1; Figs. 3, 4 and are transverse sections on the lines 33, 4--4 and 5-5 respectively in Fig. 1; Fig. 6 is a schematic representation of a transverse section through the tube for facilitating an explanation of the principles of operation; Fig. 7 is an enlarged view partly broken away showing an indirectly heated type of cathode; Fig. 8 is anend view of a permanent magnet assembly that may be used instead of a coil for Fig. 10 is a diagrammatic representation of an elemental circuit organization for the tube,

The typical tube structure illustrated as embodying the invention comprises in general a linear or filamentary type of thermionic emissive cathode K, a shield S associated with this cathode, a pair of anodes Al, A2, and a control electrode C. These tube elements are enclosed in a highly evacuated envelope E, with suitable external connections for the heating circuit of the cathode, and for connections to the control element and anodes.

In accordance with this invention, the tube is subjected to a magnetic field of the appropriate strength to provide magnetic lines of force acting axially of the cathode K and substantially parallel with the surfaces of the anodes Al, A2. As schematically illustrated in Figs. 1 to 5, this magnetic field is assumed to be provided by a magnetizing coil or solenoid B, which is disposed around the tube envelope E, and which is energized from a suitable source of unidirectional current, such as a battery. However, any suitable source of magneto-motive-force may be employed to provide the magnetic field characteristic of this invention, such as a permanent magnet assembly of upper and lower pole pieces 5, 6 and permanent magnets 1, as schematically illustrated in Figs. 8 and 9, or a structure having a magnetic circuit with enlarged pole pieces opposite the ends of the tube envelope, and including a magnetizing coil or permanent magnet.

A glass envelope E is assumed for the tube structure illustrated; and since certain types of circuit organizations for oscillators, inverters, and the like, for which this type of tube is specially adapted, involve two separate tube structures, the envelope E is shown as having a generally elliptical cross-section, with suificient curvature and thickness for the side walls to withstand pressure when evacuated, so that two tubes may be conveniently arranged side by side and subjected to the magnetic field provided by a single solenoid or permanent magnet assembly, as indicated in Fig. 8. Obviously, the tube envelope E may be circular in cross-section, or be formed of metal instead of glass, or take any one of a wide variety of forms, without departing from the invention.

As shown, the envelope E has a press [0 at the lower end in the usual form for anchoring the supports for the tube elements and providing seals for the lead-in conductors, all in accordance with the usual practice. The external connection for the control element C is sealed in the upper end of the envelope E; and the usual tubulation for exhaust may be provided at this upper end, as indicated at II. It is contemplated that this envelope E will be provided in practice with a suitable base; but since such base and other refinements of tube design to conform with recognized practice are not material to the present invention, no attempt has been made to illustrate or describe them.

In the arrangement shown in Figs. 1 to 5, the elongated or filamentary cathode K is assumed to be a strip of tungsten or thoriated tungsten of a rectangular cross-section, which is directly heated. This linear cathode K is disposed in an elongated opening or slot I2 of the cathode shield S, which is preferably formed with rectangular upper and lower end plates l4, l5, as by welding such plates to flanges on the ends of this shield S. The shield S is supported at its lower end by a supporting element l6 of an inverted L-shape to which is welded a rod l'l extending through a Seal in the press '0 to provide an external connection to the shield S.

The upper end of the cathode K is welded or otherwise secured to the cathode shield S at the upper end of the slot l2 in this shield; and the lower end of the cathode K is attached to a resilient member 20 having bends or loops therein to permit contraction in length and maintain enough endwise pull on the cathode K to keep it straight as it is heated and increases in length. This resilient member 20, which is preferably in the form of a metal or alloy capable of retaining its resiliency after being heated to a degassing temperature, is connected to a rod 2| sealed in the press ll) of the envelope. The heating circuit for the cathode K is connected to the lead-in conductor H for the heat shield S and to the lead-in conductor 2| for the resilient member 20 attached to the lower end of the cathode K, so that the heating current flows longitudinally through the cathode K and through the heating shield S to raise the cathode to the appropriate emitting temperature. Since the shield S has a substantial cross-section, it may conduct the cathode heating current without objectionable temperature rise.

Any suitable type of thermionic emissive cathode may be employed in this invention, either directly or indirectly heated, and with or without oxide coatings. In this connection, Fig. '7 illustrates schematically an indirectly heated cathode comprising a flattened tube 24 of nickel or other suitable core material having an oxide coating, such as disclosed for example in the prior patent to D. V. Edwards et al., No. 1,985,855, De-

cember 25, 1934. The emissive element of this type of cathode is indirectly heated by current in a heater wire 25 inside the tube. this heater wire being arranged as a twisted pair, or in one or more loops, or otherwise disposed in the manner characteristic of indirectly heated cathodes. This heater wire 25 is covered with a suitable heat resistant insulating material, such as aluminum oxide, and has its ends connected to leadin conductors 26 for the heating circuit sealed in the press I0. An indirectly heated and essentially equipotentia-l cathode of this character may be employed to advantage in certain types of tubes embodying this invention, where the external magnetic field characteristic of the directly heated type may have an undesirable eilect upon the desired electron movement characteristic of this invention. I

The anodes Al, A2, in the tube structure shown are flat plates of a rectangular shape disposed on opposite sides of the cathode K in the plane of its axis and in the general plane of the cathode shield S. These anodes Al, A2 are preferably formed with integral or attached end plates 28, 25 at opposite ends and with a side projection or extension 30 along the edge remote from the cathode. As shown in Fig. 4, these anodes Al, A2 are disposed such that their end plates 28, 29 and side extensions 30 extend in opposite directions from what may be termed the median plane of the tube through the axis of the cathode K, shield S, and surfaces of the anodes Al, A2, for reasons later explained. Each anode Al, A2 is supported at its lower end by a supporting rod 32 welded thereto and sealed in the press In of the envelope E.

In the structure illustrated, the upper ends of the anodes Al, A2, and the upper end of the cathode shield S are interconnected by an insulated structure as shown in Fig. 1. A rod 34, surrounded by a tube or sleeve 35 of steatite, or like heat resistant insulating material, is bent in an inverted U-shape, and its ends are welded or otherwise attached to the upper end pieces 28 of the anodes Al and A2. This insulator sleeve 35 is formed with deep narrow recesses in its ends, in accordance with the teachings of a prior application of E. K. Smith, Ser. No. 674,953, June '7, 1946, now Patent No. 2,456,540, December 14, 1948, for the purpose of maintaining the appropriate insulation between these electrodes, in spite of the accumulation of evaporated material on the surfaces of the insulator during the degassing and exhaust process. The insulator sleeve 35 is formed with a shallow peripheral groove near its middle; and a metallic strap or loop 36 fitting in this groove has its ends attached to the upper end of the cathode shield S. It should be understood that this structure shown and described is merely illustrative of an interconnection between the upper ends of these electrodes desirable to maintain the appropriate space relationship; and various other mounting and supporting arrangements for the electrodes may be employed, without departing from the invention.

The control element C in the structural arrangement shown comprises a rectangular piece of sheet metal bent into the general form of a flattened tube and welded at the overlapping edges. This control element C is supported within the envelope E largely by the frictional contact of coiled springs 38 interposed between this control element at its ends and the' inner walls of the glas envelope E, these springs 38 having their ends conveniently attached to said control element. An arched plate 39 having its ends welded to the side walls of the control electrode is attached near its middle to the lower end of a rod 40 extending through a seal in the upper end 5 of the envelope E, so as to provide an external connection to the control element.

This control electrode C, although shown in the form of a flattened tube or cylinder of sheet metal for structural simplicity and ease of degassing by induction heating, has two parallel fiat side walls; and in functional efiect this control element may be considered as providing two fiat parallel electrodes-of a rectangular shape. Such electrodes, although imperforate as shown, perform in part the functions of a grid structure in a conventional triode; and it is convenient to refer to these two fiat parallel side walls of the control electrode C as grids GI and G2.

The electrode and the various supporting elements, except those passing through the press Ill and otherwise located beyond the limits of the electrodes, are preferably formed of tantalum, molybdenum, or similar non-magnetic metal or alloy, in order that the magnetic field in the interelectrode space around the cathode K may not be weakened or distorted by the electrodes or their supporting elements, although it shoud be understood that this is primarily a matter of degree and certain operable results may be obtained under conditions where the magnetic field has a variable distribution of intensity.

In assembling the parts of the specific tube structure illustrated, the control element C with its rod 40 long enough to extend through an open ing for the seal at the top of the envelope E, is inserted in the lower open end of the envelope. the coils or turns of the springs 38 compressing and extending as necessary to conform with the inner surface of the envelope to hold the grid assembly in place. The assembly of the oath- 7 ode K, shield S and anodes Al and A2 may then be positioned inside of the control element; and after the parts have been properly aligned and the appropriate endwise pull applied to the resilient supporting element 20 for the lower end of the cathode K has been applied, the press III is formed for the lower end of the envelope in the usual manner, together with the seal for the grid lead-in rod 40 at the upper end of the envelope.

After the tube elements as above described have been mounted and sealed in the envelope, the tube is subjected to a suitable procedure for thoroughly degassing all of the parts, activating the oathode, and exhausting the envelope to obtain a high vacuum, in conformity with well known practices in the art. In a power tube of the type contemplated, the various tube elements assume relatively high temperatures in operation, and the degassing and exhaust procedure for a tube should provide for degassing all of the tube elements to a high degree, employing such structures for the tube elements and heating procedure that all parts can be effectively heated to high temperature levels while the tube is being pumped.

In discussing the nature of the invention and its contemplated mode of operation, and in explaining how the invention may be adapted and utilized in practice, it is expedient to discuss certain theories of electron emission and movement in concurrent electrical and magnetic fields, the effect of space charge, and the like, but it should be understood that the following theoretical discussion of the principles of operation is necessarily general and incomplete, and that the utility of the invention does not depend upon the accuracy or sufiiciency of the theories presented herein to explain the action and operation of a tube of this invention.

Considering some of the structural features and attributes of the tube of this invention, although the elongated or filamentary hot cathode K is capable of emitting electrons radially in all directions throughout its length, the shield S connected to this cathode and at the same potential acts to limit electron emission into the inter-electrode space from two principal emissive surfaces of the cathode K on opposite sides of its axis and opposing the surfaces of the control element or grids GI, G2. The anodes Al, A2 are disposed edgewise to the cathode K on opposite sides of its axis, with the shield S at cathode potential interposed between these anodes and the cathode. Consequently, in marked contrast to the conventional arrangement of tube elements, the potential on the anodes Al, A2 is comparatively ineffective to draw electrons from the cathode K and accelerate them toward these anodes. The particular disposition of the anodes AI, A2 withrespect to the cathode K, and the extent of shielding, may be varied somewhat according to the tube operating characteristics desired; but in general the space current in the tube of this invention is established principally by the positive potentials on the grids GI, G2 and largely independently of the potential of the anodes Al, A2. 7

Considering a transverse plane through the tube such as indicated in Fig. 6, the electrons from the upper and lower emissive surfaces of the cathode K under the influence of positive potentials on the grids GI, G2 are subjected to the combined action of an axial magnetic field and the electrostatic field established by the existing potentials on the grids GI, G2 and the anodes Al, A2. It is diflicult and impracticable to define the paths of movement or trajectories of the various electrons under the complicated and variable conditions of electrode potentials, strength of magnetic field, effect of space charge, and the like; but some general observations will serve to indicate how the combined action of magnetic and electrostatic fields may be utilized in accordance with this invention to obtain the desired result.

An electrostatic field provides a force acting upon an electron at all points in this field in a direction which is normal to the equi-potential lines of this field, and this force acts to accelerate or decelerate the electron dependent upon whether it is moving toward a. point of higher or lower potential. Althbugh the contour and spacing of such equi-potential lines of the electrostatic field for a given positive potential on the grids GI, G2 are somewhat modified by the shield S and existing positive potentials on the anodes Al, A2, it may be assumed that these equi-potential lines affecting movement of the electrons under the influence of the grid potentials are generally parallel with the surfaces of the grids GI, G2.

A magnetic field provides a force which acts upon an electron, at all points in its movement under the influence of an electrostatic field, in a direction both at right angles to the magnetic lines of force and the then existing direction of movement of the electron. For simple thinking in this respect, an electron in motion may be compared with a conductor carrying current; and it is a familiar phenomena in electrical motors and the like that a current carrying conductor disposed in a, magnetic field experiences a force tending to displace that conductor in a direction at right angles to the magnetic lines of force. While such a current carrying conductor extends in a certain direction and ordinarily has its movement restrained in some way, an electron is a freely movable charged particle and may constantly change its direction at all points in its movement to conform with the forces acting upon it due to its movement in the magnetic field. While a magnetic field may affect the instantaneous direction of movement of an electron in an electrostatic field, it does not affect the kinetic energy or total velocity imparted to such electron by the electrostatic field.

In the tube of this invention, the magnetic field is directed axially of the cathode K and generally parallel with the surfaces of the grids GI, G2. In other words, referring to a transverse plane through the tube as indicated in Fig. 6, the lines of force of thi axial magnetic field are in a direction perpendicular to the paper, as indicated by the crosses 42 in Fig. 6.

Considering the combined action of the electrostatic and magnetic fields characteristic of this invention upon electron movement in a transverse plane through the tube as indicated in Fig. 6, and assuming some positive potential on the grids GI, G2, an electron leaving the upper emissive surface of the cathode K, for example, is accelerated toward the grid GI. At the same time this electron is subjected to the influence of the axial magnetic field, and hence follows a path curving in one direction or another dependent upon the polarity of the magnetic field. If the magnetic field is strong enough for the existing positive potential on the grid GI, the electron under consideration in following such a curved path will not reach this grid, although it has acquired the same kinetic energy and total velocity as if it had moved through the same distance straight toward the grid GI. After such an electron has reached a point in its curved path where it is nearest to the grid GI, and continues its movement still following curved path, this electron is decelerated, being pulled back so to speak toward the grid GI. Thus, an electrostatic field of a positive potential on the grid GI acts in cooperation with a magnet field of appropriate strength and polarity to cause the electrons to leave the upper emissive surface of the cathode K of Fig. 6 and to follow curved paths or trajectories missing the grid GI and extending to the anode Al. Electrons from the lower emissive surface of the cathode K follows similar curved paths extending to the anode A2 under the combined influence of the magnetic field and a positive potential on the other grid G2.

With regard to the nature of the curved paths of movement or trajectories of the electrons under such conditions, if the effects of space charge, anode potentials, random initial electron velocities at the cathode, and like factors are disregarded, so that the electrostatic field is uniform, mathematical analysis shows that the electrons would follow a curve known as a cycloid, i. e. the path traced by a point on the radius of a circle rolling in a plane along a straight line in that plane. In the actual tube structure such as contemplated, the shield S, the relative potentials of the grids GI, G2 and anodes Al, A2, and other factors tend to give a field distortion causing the electron trajectories to deviate somewhat from a true cycloid. Also, each electron in following its curved path exerts a repelling force on all neighboring electrons; and this effect of space charge, more particularly adjacent the cathodes K and anodes AI, A2 where the electron velocities are low, has a scattering or defocusing effect upon the trajectory of the individual electrons, which tends to spread out or widen the beams of space current such as roughly indicated by the dotted lines 43 in Fig. 6. In spite of these variations and for lack of better terminology, it is convenient to refer to the trajectories and the curved beams of space current as being of a cycloidal nature. One significant attribute of such cycloidal beams of space current is that the electrons have a low level of velocity near the ends of the beams adjacent the anodes Al, A2.

Thus, in the tube of this invention a negative potential on the grids GI, G2 will act to repel electrons leaving the principal emissive surfaces of the cathode K and suppress space current in much the same way as space current may be cut off by a negative grid in a conventional triode, with the distinction that the potentials of the anodes AI, A2 in a tube of this invention are relatively ineffective at the emissive surfaces of the cathode, and a smaller negative grid potential for out off is required for a given anode voltage. In a conventional triode, the grid cannot be made positive without drawing grid current, which causes objectionable grid circuit losses; and it also requires driving power in the grid circuit to maintain the grid positive. In a tube of this invention, however, the axial magnetic field of appropriate strength enables relatively high positive potentials to be applied to the grids GI, G2 without significant or objectionable grid current. If other words, the space current in-the tube of this invention is established primarily by the positive potentials applied to the grids GI, G2,

largely independently of the anode t? cathode difference of the potential or tube drop voltage. Stated another way, the control element or grids GI, G2 in the tube of this invention not only perform the function of controlling the space current, but actually create the space current without much, if any, help from the anode potentials.

As previously indicated, the primary purpose of this invention is to provide an electron discharge tube of the high vacuum type which will operate at a low tube voltage, since this tube drop voltage is a measure of the losses in the tube for a give-,1 output, and the efllciency of the tube as a circuit element in a power conversion organization. In general, the tube drop voltage of a tube when conducting current in a circuit organization automatically assumes the value required to accumulate electrons at the anode of the tube at a sufficient rate to satisfy existing load conditions. For example, if a tube is capable of conducting an anode current of one ampere, and existing conditions call for this current output, the anode assumes the potential with respect to the cathode necessary to receive 628x 10 electrons per second, thereby fixing the tube drop voltage and tube losses for this operating condition.

In the conventional triode, the tube drop voltage assumes the value needed to draw electrons from the cathode past the barrier of high space charge adjacent the cathode, and move these electrons to the anode surface in opposition to the effects of space charge throughout the interelectrode space. In the tube of this invention, by way of contrast, the grids GI, G2, rather than the anodes AI, A2, act in cooperation with the axial magnetic field to establish the space current in opposition to the effects of space charge. This space current created by the control elements GI and G2 is in the form of curved beams which extend to the surfaces of the anodes Al, A2, so that all these anodes have to do is to receive or collect from these curved beams of space current such electrons as may be needed to satisfy existing load conditions for the tube. The magnetic field enables the grids GI, G2 to perform this function of establishing space current without objectionable electron current to these grids,

which occurs in the conventional triode, if the grid is made positive.

As previously indicated, the electrons in the curved beams of space current approach the anodes AI, A2 with a low level of velocity, rather than with high velocity and large kinetic energy to be absorbed by the anode, as in the conventional triode. In this connection, while the electron density and space charge in the regions adjacent the anodes AI, A2 are higher than for the anode of the conventional triode, the electrostatic fields of these positive grids GI, G2 are effective to neutralize the effect of space charge in these regions, much the same as at the oathode. In other words, the space charge has a defocusing effect upon the beams of the space current, and also determines the positive grid potentials needed for a given intensity of space current, but is not a material factor in dictating the tube drop voltage needed for a given anode current, as in the case of the conventional triode.

In the foregoing discussion, attention has been directed to the paths of movement of the electrons in transverse planes at right angles to the axis of the cathode. The initial velocities and the direction of movement of electrons leaving the surface of a thermionic emissive cathode, however, vary substantially in a random fashion; and many of the electrons emitted from the cathode K will have some component of initial velocity axially of this cathode up or down toward the ends of the tube. Since the velocity component of an electron axially of the cathode is in the same direction as the lines of force of the axial magnetic field, electron motion in such direction is not effected by the magnetic field. For example, an electron leaving the cathode K with some initial velocity axially of the tube will continue to move in that direction without any change in its velocity insofar as the magnetic field is concerned, and with relatively small change in its direction or velocity due to the electrostatic field, since its equi-potential lines are generally parallel with the axis of the tube.

Taking into consideration such random initial electron velocities axially of the tube, it can be seen that the paths of movement for a substantial number of electrons drawn from the cathode K will be such that these electrons could move out of the electrode area without contacting with the fiat surfaces of the anodes Al, A2, or contacting with the shield S, if their surfaces were limited to axial planes. It is desirable, however, that electrons emitted from the cathode K under the control of the grids GI, G2 should be collected either by the anodes Al, A2 or returned to the cathode through the shield S, since any stray electrons will ultimately reach the grids GI, G2 and cause objectionable grid current, or will bombard and overheat supporting elements or portions of the tube envelope that may be in the paths of movement of such electrons. For these reasons the anodes AI, A2 are preferably provided with upper and lower end plates 28, 29 to intercept or receive electrons having such axial components of initial velocity that they would otherwise miss the fiat surfaces of these anodes and drift outside of the electrode area. Similarly, the shield S is preferably provided with upper and lower end plates I4, I5 to collect electrons, more particularly those emitted from the end portions of the cathode K, which have such axial components of initial velocity as to escape the end plates 28, 29 of the anodes AI, A2. In short, the anodes AI and A2 and the shield S are preferably formed to intercept the electrons that would otherwise drift out of the electrode area toward the ends of the tube, so as to restrict electron movement, as for as the limitations for mechanical separation of parts will permit, to the inter-electrode region.

Referring again to the electrons moving in the curved beams of space current in transverse planes such as indicated in Fig. 6, as previously mentioned, these electrons when approaching the anodes AI, A2 will have variable velocity components normal to the surfaces of these anodes, due to variations in their initial velocity at the cathode and the defocusing effect of space charge and the like. Consequently, some of the electrons approaching the surfaces of the anodes Al, A2 may have a large component of velocity parallel with these surfaces and such a small velocity component toward these surfaces that these electrons will not be received by the anodes at their potentials then existing. Under such conditions, such electrons will continue their movement along another path of a cycloidal character under the combined influence of the magnetic field and the electrostatic field of the associated grid 12 GI, G2. In order that electrons making such a second hop, so to speak, may be intercepted by the anodes Al, A2, their surfaces may be extended and made wide enough to intercept or to receive electrons at the end of the second hop, which due to a variation in the effect of space charge on other factors may involve a somewhat different trajectory and allow the electron to reach the anode surface at the same potential.

Also, or as an alternative to extending the surfaces of the anodes AI A2, these anodes are preferaly provided with side extensions or projections 30 of the appropriate width or depth to intercept electrons that may follow successive cycloidal paths in their movement. If desired, the shield S may be modified when such side extensions 30 on the anodes Al, A2 are employed, so as to shield more effectively the principal emissive surfaces of the cathode K from the electrostatic field or these anodes, dependent upon the operating characteristics of the tube desired.

The tube of this invention may be employed in substantially the same way as a conventional triode in any suitable circuit organization for power conversion purposes, such as an oscillator, inverter, amplifier or the like, more particularly where high efficiency and low tube losses are of more significance than some particular tube operating characteristic, such as linear variation of anode current with grid and plate voltages. In using a tube of this invention in such circuit orginazitions, the control element or grids GI G2 and the anodes Al, A2 are associated with grid control and anode circuits in the same way as a conventional triode, in a manner such as sche- .matically shown in Fig. 10. The cathode K is provided with the usual heating circuit, which is shown in Fig. 10 as connected to the secondary of a heating transformer 46 with a center tap for the cathode connections of the grid control and anode circuits. The anodes AI, A2 are electrically connected together, either inside or outside the tube envelope as most convenient, and are connected to a conventional anode circuit such as shown in Fig. 10, which includes a suitable load and a battery 41 or equivalent source of anode voltage. The grid control circuit for the control element of the tube of this invention, comprising the surfaces referred to as grids GI, G2, includes the appropriate form of grid control means, indicated in block form GC in Fig. 10, which includes a source of voltage and control means for providing the desired variations in the potential of this control element with respect to the cathode.

For many applications of the tube of this invention it is desirable to include in the grid circuit a resistor 49, which may be also supplemented by a shunting capacitor 50 if desired, so that electron current to the grids GI, G2 will automatically provide a biasing voltage to reduce their positive potential. As previously explained, the tube drop voltage automatically adjusts itself in operation to the value needed to collect electrons from the curved beams of space current at a rate to satisfy the existing demand for current in the external anode circuit of the tube; and the number of electrons in the curved beams of space current is determined principally by the existing positive potential on the grids GI, G2, largely independent of the anode potential or tube drop voltage. In other words, variations in load conditions and tube drop voltage are not accompanied by similar variations in the space current in the tube, as in the conventional triode.

Consequently, under some operating conditions it may happen that the existing positive potential on the grids GI, G2 will establish more space current than needed for existing load conditions and provide more electrons than the anodes Al, A2 will collect. The surplus of electrons drawn from the cathode K are likely to reach the grids GI, G2 ultimately and cause substantial or excessive electron current to these grids, either due to the character of the trajectory of these surplus electrons, or as a result of collision with other electrons or residual gas molecules. A resistor 49 of appropriate resistance in the grid circuit of the tube, as shown in Fig. 10, with or without the shunting capacitor 50, will act automatically to control the positive potential of the grids GI, G2 in response to grid current, in the manner disclosed in the prior application of D. V. Edwards,

Ser. No. 792,071, filed December 16, 1947. This automatic rid biasing means serves to keep grid current within tolerable limits. Excessive grid current may cause undue heating of the grids GI, G2, tending to make them emissive to a degree interfering with the proper performance of the tube.

From the foregoing, it can be seen that the tube of this invention has desirable operating characteristics from the standpoint of high elliciency and low tube losses, due to the distinctive organization or arrangement of tube elements in combination with a magnetic field. It is obvious that various adaptations, modifications and additions may be made in the particular structure and arrangements of parts shown and described, without departing from the underlying principles and mode of operation characterizing the invention; and it should be understood that the particular tube structure shown and described is merely typical or representative of the various forms a tube embodying this invention may take in practice.

What I claim is:

1. An electron discharge device of' the high vacuum type operated by conduction of primary electrons and comprising in combination, a thermionic emissive cathode heated by current and associated shielding means at cathode potential for limiting electron emission into space from two principal emissive surfaces of said cathode, an anode having planar surfaces to collect electrons emitted by said cathode and disposed in planes at one side of the cathode generally parallel with its principal emissive surfaces so that its potential is comparatively ineifective to control electron emission from said cathode, a source of magneto-motive-force establishing a magnetic field directed generally parallel with the emissive surfaces of said cathode, and a control electrode having surfaces opposing said principal emissive aurfaces of said cathode and acting dependent won its potential relative to the cathode to suppress or establish the space current to be received by said anode, said magnetic circuit having a strength to direct the electrons of said space current along paths in curved beams extending to said anode surfaces but largely escaping said control electrode for a range of relatively high positive potentials thereon, whereby the space current of the tube collected by the anode is established principally by the control electrode without significant electron current thereto, and largely independently of the anode to cathode difference of potential.

2. A controllable electron discharge device operating by conduction of primary electrons and comprising in combination, a linear heated cathode capable of emitting electrons radially in all directions throughout its length, a shielding electrode at cathode potential associated with said cathode for limiting electron emission into space from two principal emissive surfaces, a source of magneto-motive-force establishing an axial magnetic field for said cathode, a control electrode establishing electrostatic fields governing electron emission from said principal emissive surfaces 01' the cathode and imparting velocity to such emitted electrons to constitute a space current to be conducted by the device, said magnetic field having a strength to direct the electrons of said space current along paths to pro-idle curved beams of space current extending radially from the cathode in opposite directions and missing said control electrode for relatively high positive potentials thereon, and an anode having surfaces collecting primary electrons emitted from said cathode and disposed transversely of said curved beams of space current near their ends where there is a low level of electron velocity under the influence of said control electrode, whereby the space current to be conducted by a tube is established principally by the potential of the control electrode and this space current is collected by the anode at a positive potential much less than required to establish that space current.

3. A controllable electron discharge device operating to conduct a space current of primary electrons with a low tube drop voltage comprising, in combination with a linear heated cathode and associated shielding electrode at cathode potential limiting electron emission into space from two principal surfaces of said cathode into beams extending radially from said cathode, an anode having extensive planar surfaces disposed on opposite sides of the axis of said cathode in approximately the same plane as said principal emissive surfaces of said cathode, a magnet establishing magnetic lines of force "axially of the cathode, and a control element cooperating with said magnetic field to establish curved beams of space current extending to said electron collecting surfaces of said anode, the electrons in said curved beams of space current under the influence of said control electrode having a low level of velocity in the region adjacent the anode surfaces, whereby said anode may collect electrons from said curved beams of space current with an anode to cathode difference of potential much less than that required to establish that space current.

4. A controllable electron discharge device for conducting substantial currents at a low voltage and having an electrode assembly within a highly evacuated envelope, said device comprising, a hot cathode and associated shield at cathode potential for emitting into space electrons from certain areas of said cathode under the influence of an electrostatic field, a control element establishing an electrostatic field to draw electrons from said areas of said shielded cathode and impart velocity to such electrons to constitute space current to be conducted by the device, a magnet providing a magnetic field directing the electrons of such space current into curved beams of a cycloidal character largely escaping said control element, and planar anode surfaces disposed edgewise with respect to said shielded cathode to have comparatively little effect upon the electron emission from the cathode but extending transversely of said beams of space current, whereby electrons may be collected from said curved beams of space current at an anode to cathode potential much less than required to establish that space current.

5. A controllable electron discharge device of the high vacuum type comprising in combination, a linear heated cathode and associated shielding electrode for providing electron emission into space radially from said cathode from certain principal emissive surfaces, mean constituting a magnetic field directed axially of said cathode, a control element having surfaces on opposite sides of the axis of said cathode opposing its principal emissive surfaces and acting to create as well as control the space current to be conducted by the device, said magnetic field having a strength with respect to the spacing between said control element and said cathode to cause the electrons of the space current to follow paths in curved beams largely escaping said control element in spite of a relatively high positive potential thereon, the electrons in said curved beams of space current being decelerated by the electrostatic field of said control element to a low level of velocity in a region midway. between its surfaces, and an anode having planar surfaces disposed in said region on opposite sides of the axis of said cathode transversely of said curved beams of space current, whereby the space current to be conducted by the tube is established principally by said control element and may be collected by the anode with a low tube drop voltage.

6. A controllable electron discharge device comprising in combination, a control element, a linear cathode and associated shielding electrode for emitting electrons into space in radial beams under the influence of electrostatic fields of said control element, said control element acting to establish as well as suppress the space current to be connected by the device, an anode having planar surfaces on opposite sides of the axis of said cathode substantially in line with said shielding electrode, and a magnet providing an axial magnetic field around the cathode to cause the electrons drawn from the cathode by said control element to follow curved paths of movement extending to said anode surfaces but largely escaping said control element for a range of relatively high positive potentials thereon.

7. An electron discharge device comprising in combination, a highly evacuated envelope, a tubular control electrode within said envelope having flattened side walls and supported principally by frictional engagement with the inner surface of said envelope, a hot filamentary cathode extending along the axis of said control electrode, anodes supported by said envelope within said control electrode on opposite sides of said cathode and having surfaces generally parallel with the side walls of said control electrode, shielding means between said cathode and anode for limiting the effect of the electrostatic field of said anodes upon said cathode, and a magnet outside of the envelope providing a magnetic field directed axially of said cathode, said control electrode cooperating with said magnetic field to establish curved beams of space current extending to said anodes but largely missing said control electrode for a range of relatively high positive potentials thereon.

8. A controllable electron discharge device comprising in combination, a linear heated cathode and associated shielding electrode limiting electron emission into space from said cathode into radial beams, said shielding electrode having surfaces extending transversely of the cath- 16 ode at its ends, a magnet providing an axial magnetic field around said cathode, an anode having planar surfaces extending parallel with the axis of said cathode substantially in line with said shielding electrode, said anode having end plates disposed transversely of the cathode, and a control element cooperating with said magnetic field to establish curved beams of space current extending to the surfaces of said anode but largely escaping said control element in spite of relatively high positive potentials thereon, said end plates on said anode intercepting electrons having velocity components axially of the oathode sufilcient to escape the planar surfaces of said anode.

9. A controllable electron discharge device comprising a linear heated cathode and associated shielding electrode, a magnet providing an axial magnetic field around said cathode, and a control electrode cooperating with said magnetic field to provide curved beams of space current, an anode having rincipal planar electron collecting surfaces disposed transversely of said curved beams of space current near their ends, said shielding electrode being interposed between said anode surfaces and said cathode, said anode also having end plates extending transversely of the cathode and side extensions projecting at a substantial angle from its principal collecting surfaces.

10. An electron discharge device comprising, a shielding electrode having a longitudinal slot therein, a filamentary heated cathode extending lengthwise of said shielding electrode within said slot, an anode having surfaces on opposite sides of said cathode disposed on opposite sides of said shielding electrode and edgewise thereto, a magnet providing an axially magnetic field for said cathode, and a control electrode cooperating with said magnetic field to provide curved beams of space current extending to said anode surfaces.

11. An electron discharge device comprising, an elongated tubular control electrode, a magnet providing a magnetic. field directed along the axis of said control electrode, a heated filamentary cathode and shielding electrode disposed along the axis of said control electrode, one end of said cathode being connected to said shielding electrode, a resilient supporting element for the other end of said cathode, and anodes on opposite sides of said cathode having principal electron collecting surfaces substantially in line with said shielding electrode and being comparatively ineffective to control the potential adjacent the cathode, said shielding electrode and anodes having end plates to intercept electrons having velocity components axially of the cathode, said control element cooperating with said magnetic field to provide curved beams, of space current extending to said anode surfaces but largely escaping said control element for a range of relasaid cathode, a magnet providing a magnetic field axially of the cathode, and a control electrode cooperating with said magnetic field to provide curved beams of space current extending to said anode surfaces but largely escaping said control electrode, said anodes having end plates and side extensions for intercepting electrons 17 having substantial components of velocity parallel with said anode surfaces.

13. An electron discharge device comprising, a linear heated cathode and associated shielding electrode for emitting electrons in radial beams, a magnet establishing magnetic lines of force axially of said cathode, an anode having planar electron collecting surfaces disposed edgewise and substantially in line with said shielding electrode on opposite sides of the axis of said cathode, and a control electrode cooperating with said magnetic field to provide curved beams of space current extending to said anode surfaces, said shielding electrode and said anode having end plates extending transversely of the axis of the cathode for intercepting electrons with axial velocity components suflicient to escape the planar electron collecting surfaces of said anode.

14. A controllable electron discharge device comprising, in combination with a linear heated cathode and a magnet providing an axial magnetic field around said cathode, an anode having electron collecting surfaces, a control element acting largely independently of the potential of said anode in cooperation with said magnetic field to establish curved beams of space current extending to said anode surfaces, said control element having a resistor in its control circuit connected to the cathode for automatically reducing its positive potential as it receives electrons not collected by said anode.

15. A controllable electron discharge device operating with a low tube drop voltage comprising, a linear cathode of flattened cross-section affordlng two substantially parallel principal emissive surfaces, an anode having extensive planar sur- 18 faces in approximately the same plane as said principal emissive surfaces of said cathode, a shielding electrode between said cathode and said anode shielding said principal emissive surfaces of the cathode from the electrostatic field of said anode, a control electrode having extensive planar surfaces opposite and generally parallel with said principal emissive surfaces of said cathode, said control electrode acting in accordance with its potential to suppress or establish space current to be conducted by the device largely independent of the anode potential, and a source of magneto-motiveforce creating a magnetic field axially of said cathode, said magnetic field having a strength with respect to the spacing between said control electrode surfaces and said cathode to direct electrons along paths in curved I beams largely escaping said control electrode in spite of relatively high positive potentials thereon, said control electrode and said shielding electrode having surfaces intercepting electrons having velocity components lengthwise of the oathode sufiicient to escape saidplanar surfaces of said anode.

WARREN G. BROWN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,816,682 Langmuir July 28, 1931 2,146,607 Van Overbeek Feb. 7, 1939 2,164,892 Banks July 4, 1939 2,293,177 Skellett Aug. 18, 1942 

